Various duct-connecting systems are known for connecting sections of heating and air conditioning sheet metal ducts. The duct sections may be formed of galvanized sheet steel, typically of 18-26 gauge thickness. Commonly, the duct sections are of rectangular cross-sectional shape and have integral transverse flanges at an end.
Well-known examples of such transverse duct flange connecting systems include the Transverse Duct Connector (TDC) and Transverse Duct Flange (TDF) systems. In FIG. 1, there appears a fragmentary view of a rectangular duct section 10 employing an exemplary TDC or TDF type flange system. The duct section 10 includes transversely extending flange members 12 extending from each of the duct walls 14. Each flange member 12 includes a first portion 16 extending perpendicular to the elongate or axial direction of the duct. The radially outward edges of the flanges 12 are bent back to form an upstanding, axially-extending lip 18 which extends parallel to the sides 14 of the duct section 10 from which the flanges transversely project to form a generally channel-shaped flange. In the well-known TDC/TDF system, each of the lips 18 is formed of a fold of metal to double the effective thickness of the lip 18 to provide additional reinforcement.
Because the sides 14, transverse flange portion 16, and lips 18 of each duct section 10 are all integrally formed from a single sheet of metal, the flange members 12 do not extend around the corners of the duct sections. Accordingly, right-angle shaped corner connectors 20 having apertures 22 adapted to receive fasteners, such as bolts, are used as the primary means of connecting adjacent duct sections together. The corner connectors each have a pair of legs 24 intersecting at right angles. The two perpendicular legs of the corner connector 20 are seated upon the surfaces of adjacent, mutually perpendicular flange members 12 projecting from adjacent sides 14 of the duct section 10. A peripheral rib or ridge 26 may be formed in the duct wall 14 to facilitate seating or a snap-fit retention of the corner connector 20 within the flange 12. A side cross-sectional view of a corner connector 20 seated within a flange 12 is shown in FIG. 2.
Although only a single corner of a single duct section 10 is shown for ease of illustration, it will be recognized that four corner angle fasteners 20 will be seated on the flanges at each end of a duct section 10 for coupling to another duct section. Likewise, four additional corner angle fasteners 20 will be seated within like flanges on the other duct section to be joined. Bolts are then passed through each pair of facing corner angle fasteners, thereby compressing the flanges at the abutting ends of the joined duct sections.
To prevent the corner connectors from becoming dislodged from the transverse duct flange, e.g., during transport or handling, it is common to secure the corner connectors 20 to the flanges 12 by bending the upstanding lips 18 projecting from the flanges over the corresponding aligned portions of the legs 22 of the corner connectors to form a crimped connection 26 between the flange 12 and corner connector 20. Commonly, a hammer or mallet is used to bend a portion of the flange lip 18 over the right angle connector legs 24. U.S. Pat. No. 4,713,959 discloses a tong- or pliers-like hand tool having specially shaped jaws for bending the upstanding flange lips of a transverse duct flange over the legs of the corner connectors. The tool disclosed in U.S. Pat. No. 4,713,959 is said to overcome noise and efficiency problems associated with pounding over the flange lips using a hammer.
A disadvantage of the above-mentioned pliers-type of crimping tools is that they require that a high amount of force be applied by the user, particularly when used with ducts formed of heavier gauges of sheet metal, such as 18 or 20 gauge. The force required is such that some operators lack sufficient physical strength to perform a bending or crimping operation. Even where the operator possesses a sufficient degree of strength to perform a crimping operation with a pliers-type crimping tool, the stresses applied to the tool due to the degree of force required to bend over the flange lips makes such prior art tools highly susceptible to breakage.
What is needed, therefore, is a crimping tool and method for securing a corner connector to a transverse duct flange which is less physically demanding on the operator and which is suited for use with all gauges of sheet metal, including heavier gauges such as 18 and 20 gauge thicknesses. The present invention contemplates an improved duct flange crimping tool and method which overcome the above-referenced limitations and others.